Further thoughts about human reason from God’s Word:
No wisdom, no understanding, no counsel can avail against the LORD. -Proverbs 21:30
Trust in the LORD with all your heart,
and do not lean on your own understanding.
In all your ways acknowledge him,
and he will make straight your paths.
Be not wise in your own eyes;
fear the LORD, and turn away from evil.
It will be healing to your flesh
and refreshment to your bones.
For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppressed the truth. For what can be known about God is plain to them, because God has shown it to them. For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse. For although they knew God, they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened.
Claiming to be wise, they became fools, and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things.
There is therefore now no condemnation for those who are in Christ Jesus, for the law of the Spirit of life has set you free in Christ Jesus from the law of sin and death. For God has done what the law, weakened by the flesh, could not do. By sending his own Son in the likeness of sinful flesh and for sin, he condemned sin in the flesh, in order that the righteous requirements of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit. For those who live according to the flesh set their minds on the things of the flesh, but those who live according to the Spirit set their minds on the things of the Spirit. For to set the mind on the flesh is death, but to set the mind on the Spirit is life and peace. For the mind that is set on the flesh is hostile to God, for it does not submit to God’s law; indeed, it cannot. Those who are in the flesh cannot please God.
-Romans 8:1-8 (emphasis added)
The human ego wants to say that we, mankind, know and understand what is and isn’t true, what is and isn’t good. According to the God who made the universe, we have it backwards. Not only does human reason, that which we have in our own earthly bodies, on its own, not understand the truth, but it does not have the power to do so.
It is well and good to be able to point to reasons that bear witness to your faith, but reason isn’t going to argue someone who hates God into belief, only God’s Word can do that, because literally, the person you’re reasoning with does not have the mental, physical, or spiritual ability to go from their hatred to belief.
How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching? As it is written, “How beautiful are the feet of those who preach the good news!” But they have not all obeyed the Gospel. For Isaiah says, “Lord, who has believed what he has heard from us?” So, faith comes from hearing, and hearing from the word of Christ.
-Romans 10:14-17 (emphasis added)
I can talk about thermodynamics, cause and effect, punctuated equilibrium, conformist versus dynamic geological theories, and I can do it fairly well. I once had an atheist Ph.D. in microbiology tell me I put together the best presentation of the Christian side he had ever encountered.
But that doesn’t matter, because neither my reasons for God nor his reasons against had the power to change his mind.
Only the Gospel has the ability to create faith, and it cannot do that if we cannot preach it. There’s the cutesy phrase, “Preach the Gospel, if necessary, use words.” and that’s completely false because it also puts the emphasis on our deeds, our participation.
The Koine Greek of Romans 10:17 says that faith comes from the spoken word of Christ. In truth, even our human understanding of evangelism is backwards. Preach Christ, and THEN if necessary show them, because our best showing will always be tainted by our as-yet-incomplete regeneration in Christ, but the price paid on the Cross is complete and perfectly sufficient, death defeated, and eternal life won.
So, tell them.